Rationale
In pigment color inspection, colorimeters and cuvettes are two core tools that measure and evaluate colors based on different physical principles. The colorimeter is a photoelectric integral instrument, the working principle is to simulate the human eye's induction of the three primary colors of red, green and blue, through the built-in light source to irradiate the sample, the sensor receives the reflected light, and according to the chromaticity system specified by the International Commission on Illumination (CIE), the light signal is converted into a digital chromaticity value, such as L*a*b* value. Among them, L* represents luminosity, a* represents red-green chromaticity, and b* represents yellow-blue chromaticity. The calculation of chromatic aberration ΔE is usually based on the CIELAB chromatic aberration formula:
ΔE = √[(ΔL*)² + (Δa*)² + (Δb*)²]
This formula quantifies the overall color difference between the sample and the standard color. The core function of the cuvette, also known as the standard light source box, is to provide a stable, uniform, and standard-compliant lighting environment, such as D65 daylight or A light source, to eliminate the interference of ambient light variations on visual evaluation and ensure that inspectors perform visual colorimetric under consistent conditions.
Application and division of labor
In the production and use of pigments, the application of colorimeters and cuvettes has its own focus and complements each other. Colorimeters are mainly used for objective and quantitative color quality control. For example, before a batch of pigments leaves the factory, it is possible to quickly determine whether the color of the product is within the tolerance range by measuring the ΔE value of the color difference between it and the standard sample. This digital evaluation avoids the bias caused by human visual fatigue and subjectivity, and is particularly suitable for industries where color consistency is critical, such as automotive coatings, architectural coatings, and printing inks.
The cuvette mainly serves the subjective and qualitative visual evaluation link. When pigments are applied to final products (such as plastic products and textiles), their color perception may be affected by material texture, gloss, etc. Under the standard light source of the cuvette, inspectors can more accurately assess the actual application of pigments, isomeric phenomena (i.e., two colors matching under one light source and not under another), and subtle hue shifts. This is often a necessary supplementary verification step after instrument measurements.
To ensure the accuracy and comparability of the test results, the measurement and observation conditions must be strictly controlled. For colorimeters, the measurement geometry (e.g., 45°/0° or d/8°), light source type, calibration status, and sample preparation (e.g., uniformity and thickness of the pigment coating) are the main influencing factors. For cuvettes, the color rendering index, illuminance uniformity, and viewing angle (typically 45°) of the light source are crucial. Domestic and international standards, such as GB/T 3979, ASTM D1729, and ISO 3664, clearly define these conditions.
The following table compares the core application characteristics of both tools:
| Evaluation dimensions | Chromatic difference instrument |
| Core features: | Quantitative color measurement and chromatic aberration calculation |
| Output results | Digitized chromaticity values (e.g. L*, a*, b*) and ΔE values |
| Key benefits: | Objective, fast, repeatable, and data traceable |
| Limitations | It is not sensitive to appearance factors such as gloss and texture |
| Evaluation dimensions | Cuvette |
| Core features: | Provide a visual evaluation environment under standard light sources |
| Output results | Subjective visual judgment and description |
| Key benefits: | Evaluate complex appearance effects and isomeric phenomena |
| Limitations | The results were influenced by the subjective experience of the observer |
An efficient pigment color inspection process often integrates instrumental measurement with visual evaluation. The recommended process is: first, prepare pigment samples in a standard environment; Secondly, the calibrated colorimeter was used for preliminary quantitative screening to screen out samples with ΔE within the acceptable range. These samples are then placed with the standard in a compliant cuvette for final visual confirmation by experienced inspectors under a designated light source, with a particular focus on texture and color differences that the instrument cannot capture. This "instrument-oriented, human eye-assisted" mode takes into account efficiency and reliability, and is a common solution to ensure the color quality of pigments.
References
National Color Standardization Technical Committee. Measurement method of object color. GB/T 3979-2008.
ASTM International. Standard Practice for Visual Appraisal of Colors and Color Differences of Diffusely-Illuminated Opaque Materials. ASTM D1729-2016.
International Organization for Standardization. Graphic technology and photography — Viewing conditions. ISO 3664:2009.
Billmeyer, F. W., & Saltzman, M. Principles of Color Technology. 3rd ed. New York: Wiley-Interscience.